Feeling the burn? That muscle burn you feel during an intense workout is due to the buildup of lactic acid in the muscles. Lactic acid is the cause of the temporary burn during an active workout; it is not (contrary to popular belief) the primary cause of your muscle soreness for the hours and days post-workout.
What does cause muscle soreness after a workout?
The muscle soreness you experience for days after a workout—the kind that makes it difficult to move—is generally caused by an influx of white blood cells in the muscle tissue, resulting in inflammation in the muscles. During intense exercise, such as a weight-lifting workout, your muscles experience microscopic damage in the myofibrils (small protein contractile units of the muscles). This damage is a normal part of muscle growth and is different from large-scale damage you might experience with an injury.
To heal the muscle damage that causes soreness, the muscles need nutrients and fluid—which is why eating protein and drinking plenty of water after a workout is important. The healing process can last anywhere from a few hours to a few days, depending on the intensity of your workout and the extent of that microscopic muscle damage.
Soreness isn’t necessary to induce muscle growth, but many people take muscle soreness as a sign of a good, hard workout.
About lactic acid buildup—what causes it?
Temporary lactic acid buildup during an active workout is essentially the result of poor oxygen flow to the muscles during a workout. A hard workout requires more oxygen and energy production that your body can adequately deliver, so there are systems in place to get energy from other sources (energy generated anaerobically, or without oxygen).
In an anaerobic workout, the body produces energy from glucose that is broken down and metabolized into pyruvate, which then turns into lactate, allowing the glucose breakdown and energy production to continue. This process can continue at high rates for one to three minutes during an intense workout, and during this time, the lactate accumulates in high levels in the muscles.
That acidity from a buildup of lactate, or lactic acid, is what causes the burning sensation you experience during intense exercise, and it typically goes away after a few minutes of recovery.
How can I reduce muscle soreness during and after a workout?
Pace yourself as you increase the duration and intensity of your workouts. If you aren’t used to working out, don’t jump right into intense, hour-long workouts every day of the week. Gradually increase the time and intensity of your workouts, allowing your body’s lactate threshold to increase.
After a workout, drink plenty of water to help eliminate excess acid. Eat a balanced diet rich in fruits, vegetables, whole grains and lean sources of protein to help restore your muscles, and get plenty of rest. Without adequate sleep and periods of rest, your muscles will not have a chance to repair themselves.
While many athletes work off the mantra “no pain, no gain,” it’s important to keep in mind that muscles soreness from lactic acid and the temporary breakdown of muscle fiber is different from true pain. If you experience pain during a workout, stop what you are doing and talk with a trainer or see your doctor. Pain is often an indicator of an injury. Learn to distinguish between muscle soreness and true pain.